278 
PALAEONTOLOGY OF NEW YORK. 
Section b.—Slender forms. 
Orthoceras Marcellense. 
PRATES XXXVIII, FIGS. 4, 5, 6, 7, 9; LXXXIII, FIGS. 1-10, 12; CXIII, FIG. 18. 
Marcellus orthocera, Vanuxem. Geolog. Surv! of N. Y.: Report of the Third District, p. 147. 1842. 
Oithoceras tyjms, Saemann. Dunker and von Myer. Palseontographica, Dritter Band, 3. Lieferung, p. 165, 
pi. 20. 1853. 
“ Marcellansis (Vanuxem), Hall. Thirteenth Rep N. Y. State Cab. Nat. Hist., p. 106. 1860. 
typum (Saemann), Hall, in part. Illustrations of Devonian Fossils : Cephalopoda. Explanation 
of pi. 38. 1876. 
“ Marcellense, Vanuxem. Catalogue Am. Pal. Fossils, S. A. Miller, p. 175. 1877. 
Shell straight, extremely elongate, very regularly and gradually expanding 
from the apex to the aperture. Transverse section circular. Apical angle 
varying from six to eight degrees in specimens apparently undisturbed by 
compression. Initial extremity very acute; the remaining characters are 
obscure. 
Chamber of habitation well developed, having a length of about four times 
the diameter at the last septum, regularly expanding to a point near the 
aperture where there is a very gentle constriction. Air-chambers numerous, 
about sixty in the length of the tube; regularly increasing in depth from 
the apex to the outer chamber, having a depth of about ten mm. near the 
grand chamber. 
Septa thin, with a variable concavity, usually equal to an arc of about 
115°. Sutures straight, or sometimes slightly oblique. On the convex side 
of the septa, near the chamber of habitation, there is a simple areola sur¬ 
rounding the insertion of the sipliuncle. Towards the apex this areolar 
marking is much thickened and elevated, with a prominent process, extending 
to the ventrum (pi. 83, figs. 4, 5); the whole having a furrowed and pitted 
margin, and surrounded by radiating, vascular markings over the septa (pi. 
83, figs. 6, 7). 
The process, extending to the ventral margin, is continued, as shown in 
the cast of the interior of the tube, along the ventral walls of the air-cham¬ 
bers, and sometimes along a portion of the grand chamber, as a carina. 
Sometimes this central line has a similar, smaller carina on each side, 
